"When a hermit crab spots a new shell, it'll size up the shell for a good fit. If the shell is too big, the prospecting hermit crab will sit back and wait to steal the castoff shell of a larger crab that decides to upgrade. In the meantime, while the first crab waits, other crabs gather around the shell and do the same. When a crab large enough to fit the vacant shell arrives, a bit of orderly chaos ensues."